Simon Cameron (March 8, 1799-June 26, 1889) was United States Secretary of War for Abraham Lincoln from 1861 to 1862. A political boss of Pennsylvania, his son James Donald Cameron (1833-1918) succeeded him in the Senate and as a political power in his state.

Cameron was born in Maytown, Pennsylvania. He was orphaned at nine and later apprenticed to a printer before entering the field of journalism. He was editor of the Bucks County Messenger in 1821. A year later, he moved to Washington and studied political movements while working for the printing firm of Gales and Seaton. He married Margaret Brua and returned to Harrisburg, Pennsylvania where he purchased and ran the Republican in 1824.

Cameron served as state printer of Pennsylvania from 1825 until 1827 and was state adjutant general in 1826. He constructed several rail lines and merged them into the Northern Central Railroad. He founded the Bank of Middletown in 1832 and engaged in other business enterprises. In 1838, he was appointed as commissioner to settle claims of the Winnebago Indians.

He became a Whig Party member, and later became a member of the Democratic Party, before being elected to replace James Buchanan in the Senate in 1845, where he served for 18 years (1845-49; 1857-61; 1867-77). He switched to the Republican Party and was nominated for President, but gave his support for Lincoln at the Republican National Convention of 1860. Lincoln, appreciative of Cameron's support, named him Secretary of War. Cameron administered the War Department with such favouritism that Lincoln replaced him with Edwin M. Stanton (Jan. 11, 1862), and he was censured for his conduct by the House of Representatives. Lincoln then appointed him minister to Russia, from which post he resigned (Nov. 8, 1862).

In 1867, Cameron was again elected to the Senate and served there until 1877. He was chairman of the Foreign Relations Committee from 1872 and wielded such power in Republican circles that he was able to obtain the appointment of his son as secretary of war by President Ulysses S. Grant. When, however, the new president, Rutherford B. Hayes, refused to continue the younger Cameron in office in 1877, the elder resigned his Senate seat to enable his son to succeed him.

He retired to his farm in Donegal Springs, Pennsylvania where he died on June 26, 1889.

Cameron County, Pennsylvania and Cameron Parish, Louisiana are named in his honor. The saying "An honest politician is one who, when he is bought, will stay bought" is attributed to him.